A method of the above kind is disclosed, for example, in U.S. Pat. No. 5,890,474 and in U.S. patent application Ser. No. 09/263,787, filed Mar. 5, 1999.
The check of the operability which takes place only when the vehicle is at standstill requires a checking time, measuring time or diagnostic time of 5 minutes or more for a vehicle having a very large tank volume such as a tank volume of from 80 to 100 liters. A check or diagnostic time which is so long is unwanted because it cannot be ensured during this time that the check operation is in any way disadvantageously affected. Checking as to the operability takes place when the vehicle is at standstill. If, for example, a check is started during a short stop of the vehicle such as at a traffic light of the like, then, in most cases, the time in which the vehicle is stopped is not sufficient in order to undertake a complete check of the operability of the tank-venting system.